1. Technical Field
The disclosure relates to a cooling system for an engine.
2. Description of Related Art
Generally, there is suggested a cooling system for an engine including a first coolant circuit, a second coolant circuit, a thermostat, a valve, a first coolant temperature sensor, a second coolant temperature sensor and an engine cooling control unit (see, for example, Japanese Patent No. 4883225). The cooling system determines whether there is a stuck-closed failure in the valve based on a temperature difference between a first coolant temperature that is detected by the first coolant temperature sensor and a second coolant temperature that is detected by the second coolant temperature sensor. The first coolant circuit includes a main path and a bypass path. The main path passes through a water pump, the engine, a radiator and the thermostat. The bypass path branches off from the main path between the engine and the radiator, passes through the valve and a heater core, and merges into the main path at the thermostat. The second coolant circuit branches off from the main path between the water pump and the engine in the main path, and merges into the bypass path between the valve and the heater core in the bypass path. The thermostat constantly permits flow of coolant from the bypass path to the water pump side of the main path, and opens or closes in response to the temperature of coolant after passage of the heater core to permit or prohibit flow of coolant from the radiator side of the main path to the water pump side of the main path. The valve is controlled by the engine cooling control unit. The first coolant temperature sensor detects the temperature of coolant inside the engine as a first coolant temperature. The second coolant temperature sensor detects the temperature of coolant flowing into the heater core as a second coolant temperature. In this cooling system for an engine, it is determined that there is a stuck-closed failure in the valve when a temperature difference between the first coolant temperature and the second coolant temperature is larger than an abnormality determination value while a command to open the valve is issued.
In the thus configured cooling system for an engine, it is conceivable that the temperature difference between the first coolant temperature and the second coolant temperature varies between when the thermostat is closed and when the thermostat is open while the valve is normally open because the amount of coolant flowing through the bypass path after passage of the engine varies. For this reason, if the threshold is set to a uniform value, it may not be possible to accurately detect a stuck-closed failure when there is actually a stuck-closed failure in the valve or erroneously detect a stuck-closed failure when there is actually no stuck-closed failure in the valve.